Metabolic versatility of anaerobic sludge towards platform chemical production from waste glycerol.

Waste glycerol is produced in excess by several industries, such as during biodiesel production. In this work, the metabolic versatility of anaerobic sludge was explored towards waste glycerol valorization. By applying different environmental (methanogenic and sulfate-reducing) conditions, three distinct microbial cultures were obtained from the same inoculum (anaerobic granular sludge), with high microbial specialization, within three different phyla (Thermodesulfobacteriota, Euryarchaeota and Pseudomonadota). The cultures are capable of glycerol conversion through different pathways: (i) glycerol conversion to methane by a bacterium closely related to Solidesulfovibrio alcoholivorans (99.8% 16S rRNA gene identity), in syntrophic relationship with Methanofollis liminatans (98.8% identity), (ii) fermentation to propionate by Propionivibrio pelophilus strain asp66 (98.6% identity), with a propionate yield of 0.88 mmol mmol-1 (0.71 mg mg-1) and a propionate purity of 80-97% and (iii) acetate production coupled to sulfate reduction by Desulfolutivibrio sulfoxidireducens (98.3% identity). In conclusion, starting from the same inoculum, we could drive the metabolic and functional potential of the microbiota towards the formation of several valuable products that can be used in industrial applications or as energy carriers. KEY POINTS: Versatility of anaerobic cultures was explored for waste glycerol valorization Different environmental conditions lead to metabolic specialization Biocommodities such as propionate, acetate and methane were produced.

Integrated methodology for gas content assessment and prediction in shallow muddy lake sediments: acoustic mapping and correlation analysis.

This paper provides a step-by-step description of integrated methodology for quantification and prediction of gas (methane, CH4) content dynamics in shallow aquatic sediments under changing spatial and temporal conditions. Presence of gas bubbles even in small concentrations significantly affects sediment compressibility, which in turn decreases sound speed in sediment. Our integrated methodology consists of two basic steps. In the first step, free gas content is evaluated by acoustic applications based on the sound speed inferred from the reflection coefficient from gassy bottom. The experimental bottom reflections are registered and compared to the simulated ones, using a geoacoustic inversion technique. The best match between the model and the experiment provides sediment sound speed estimate, which is converted into free gas content using a basic relation. In the second step, a multivariate linear regression is fitted for gas content and closed form expression of gas content dependence on the following predictors, which change spatially and temporally over the aquatic ecosystem, is obtained: 1) water depth, 2) short-leaving CH4 production rate peaks fueled by punctuated organic matter deposition; and 3) CH4 bubble dissolution rates.•Gas content and sound speed in the sediment are estimated via the geoacoustic inversion technique by matching the experimentally recorded and simulated bottom reflections•Only single source and receiver are required for the acoustic methodology•A multivariate linear regression is fitted for gas content to indicate its dependence on various predictors that change spatially and temporally over the lake.

Methane saline suppresses ferroptosis via the Nrf2/HO-1 signaling pathway to ameliorate intestinal ischemia-reperfusion injury.

OBJECTIVES: Intestinal ischemia-reperfusion (I/R) injury is a multifactorial and complex clinical pathophysiological process. Current research indicates that the pathogenesis of intestinal I/R injury involves various mechanisms, including ferroptosis. Methane saline (MS) has been demonstrated to primarily exert anti-inflammatory and antioxidant effects in I/R injury. In this study, we mainly investigated the effect of MS on ferroptosis in intestinal I/R injury and determined its potential mechanism. METHODS: In vivo and in vitro intestinal I/R injury models were established to validate the relationship between ferroptosis and intestinal I/R injury. MS treatment was applied to assess its impact on intestinal epithelial cell damage, intestinal barrier disruption, and ferroptosis. RESULTS: MS treatment led to a reduction in I/R-induced intestinal epithelial cell damage and intestinal barrier disruption. Moreover, similar to treatment with ferroptosis inhibitors, MS treatment reduced ferroptosis in I/R, as indicated by a decrease in the levels of intracellular pro-ferroptosis factors, an increase in the levels of anti-ferroptosis factors, and alleviation of mitochondrial damage. Additionally, the expression of Nrf2/HO-1 was significantly increased after MS treatment. However, the intestinal protective and ferroptosis inhibitory effects of MS were diminished after the use of M385 to inhibit Nrf2 in mice or si-Nrf2 in Caco-2 cells. DISCUSSION: We proved that intestinal I/R injury was mitigated by MS and that the underlying mechanism involved modulating the Nrf2/HO-1 signaling pathway to decrease ferroptosis. MS could be a promising treatment for intestinal I/R injury.

Loss of microbial diversity increases methane emissions and arsenic release in paddy soils.

Microorganisms are vital to the emission of greenhouse gases and transforming pollutants in paddy soils. However, the impact of microbial diversity loss on anaerobic methane (CH4) oxidation and arsenic (As) reduction under flooded conditions remains unclear. In this study, we inoculated microbial suspensions into natural As-contaminated paddy soils using a dilution approach (untreated, 10-2, 10-4, 10-6, 10-8 dilutions) to manipulate microbial diversity levels. The results revealed that the 10-4 and 10-6 dilutions resulted in the highest CH4 emissions (97.0 µmol and 102.3 µmol) compared to untreated groups (27.6 µmol). However, anaerobic CH4 oxidation was not observed in 10-4 dilution groups and higher dilutions, suggesting the loss of diversity inhibited the natural reduction of CH4. Moreover, the porewater As concentration in the dilution groups was 1.8-8.2 times greater than in the untreated groups. The loss of microbial diversity promoted the reductive dissolution of iron (Fe) minerals bearing As, leading to increased concentrations of Fe(II) and dissolved organic carbon (DOC), which further enhanced As release (Fe(II), R = 0.9, p < 0.001) (DOC, R = 0.8, p < 0.001) from soil to porewater. However, CH4-dependent As(V) reduction was almost entirely inhibited under diversity loss. The decline in microbial diversity increased the relative abundances of methanogens (e.g., Methanobacterium and Methanomassiliicoccus), Fe(III)/As(V)-reducing bacteria (e.g., Bacillus, Clostridium_sensu_stricto_10, and Geobacter), and the related functional genes (i.e., mcrA and Geo). These findings suggest that microbial diversity is critical for specialized soil processes, highlighting the detrimental effects of biodiversity loss on CH4 emissions and As release in As-contaminated paddies.

Effects of cashew nutshell liquid on milk production and methane emission of dairy cows in a farm condition.

This study aimed to clarify the efficacy of cashew nutshell liquid (CNSL) in methane emissions, milk production, and rumen fermentation of lactating cows in practical conditions. Ten Holstein lactating cows were used in a free-stall barn with a milking robot. Two treatments were arranged as control (no CNSL additive, n = 5) or CNSL addition (10 g/day of CNSL, n = 5) for 21 days after the 7-day preliminary period. A sniffer method was applied to predict daily methane production and methane conversion factor (MCF). In vitro, rumen gas production was also tested using the rumen fluid of individual cows. Daily dry matter intake (DMI), eating time, milk production, and methane production were not affected by the CNSL addition. However, methane production per DMI and MCF were lower (p ≤ 0.01) for the CNSL cows than those for the control cows. Ruminal total volatile fatty acid (VFA) concentration and acetate proportion tended to be lower (p < 0.15) for CNSL cows. A tendency to decrease (p < 0.10) in methane was also observed in the in vitro incubation with the rumen fluid obtained from the CNSL cows compared with those from the control cows. These results suggest that adding CNSL to diets could reduce the methane yield of cows in practical conditions.

Investigating the Metal-TiO2 Influence for Highly Selective Photocatalytic Oxidation of Methane to Methanol.

Methane conversion to valuable chemicals is a highly challenging and desirable reaction. Photocatalysis is a clean pathway to drive this chemical reaction, avoiding the high temperature and pressure of the syngas process. Titanium dioxide, being the most used photocatalyst, presents challenges in controlling the oxidation process, which is believed to depend on the metal sites on its surface that function as heterojunctions. Herein, we supported different metals on TiO2 and evaluated their activity in methane photooxidation reactions. We showed that Ni-TiO2 is the best photocatalyst for selective methane conversion, producing impressively high amounts of methanol (1.600 µmol·g-1) using H2O2 as an oxidant, with minimal CO2 evolution. This performance is attributed to the high efficiency of nickel species to produce hydroxyl radicals and enhance H2O2 utilization as well as to induce carrier traps (Ti3+ and SETOVs sites) on TiO2, which are crucial for C-H activation. This study sheds light on the role of catalyst structure in the proper control of CH4 photoconversion.

Hydrogen-independent CO2 reduction dominates methanogenesis in five temperate lakes that differ in trophic states.

Emissions of microbially produced methane (CH4) from lake sediments are a major source of this potent greenhouse gas to the atmosphere. The rates of CH4 production and emission are believed to be influenced by electron acceptor distributions and organic carbon contents, which in turn are affected by anthropogenic inputs of nutrients leading to eutrophication. Here, we investigate how eutrophication influences the abundance and community structure of CH4 producing Archaea and methanogenesis pathways across time-resolved sedimentary records of five Swiss lakes with well-characterized trophic histories. Despite higher CH4 concentrations which suggest higher methanogenic activity in sediments of eutrophic lakes, abundances of methanogens were highest in oligotrophic lake sediments. Moreover, while the methanogenic community composition differed significantly at the lowest taxonomic levels (OTU), depending on whether sediment layers had been deposited under oligotrophic or eutrophic conditions, it showed no clear trend in relation to in situ distributions of electron acceptors. Remarkably, even though methanogenesis from CO2-reduction was the dominant pathway in all sediments based on carbon isotope fractionation values, taxonomic identities, and genomes of resident methanogens, CO2-reduction with hydrogen (H2) was thermodynamically unfavorable based on measured reactant and product concentrations. Instead, strong correlations between genomic abundances of CO2-reducing methanogens and anaerobic bacteria with potential for extracellular electron transfer suggest that methanogenic CO2-reduction in lake sediments is largely powered by direct electron transfer from syntrophic bacteria without involvement of H2 as an electron shuttle.

Optimizing anaerobic digestion: Benefits of mild temperature transition from thermophilic to mesophilic conditions.

Anaerobic digestion (AD) plays a significant role in renewable energy recovery. Upgrading AD from thermophilic (50-57 °C) to mesophilic (30-38 °C) conditions to enhance process stability and reduce energy input remains challenging due to the high sensitivity of thermophilic microbiomes to temperature fluctuations. Here we compare the effects of two decreasing-temperature modes from 55 to 35 °C on cell viability, microbial dynamics, and interspecies interactions. A sharp transition (ST) is a one-step transition by 20 °C d-1, while a mild transition (MT) is a stepwise transition by 1 °C d-1. We find a greater decrease in methane production with ST (88.8%) compared to MT (38.9%) during the transition period. ST mode overproduced reactive oxygen species by 1.6-fold, increased membrane permeability by 2.2-fold, and downregulated microbial energy metabolism by 25.1%, leading to increased apoptosis of anaerobes by 1.9-fold and release of intracellular substances by 2.9-fold, further constraining methanogenesis. The higher (1.6 vs. 1.1 copies per gyrA) metabolic activity of acetate-dependent methanogenesis implied more efficient methane production in a steady mesophilic, MT-mediated system. Metagenomic binning and network analyses indicated that ST induced dysbiosis in keystone species and greatly enhanced microbial functional redundancy, causing loss of microbial syntrophic interactions and redundant metabolic pathways. In contrast, the greater microbial interconnections (average degrees 44.9 vs. 22.1) in MT at a steady mesophilic state suggested that MT could better maintain necessary system functionality and stability through microbial syntrophy or specialized pathways. Adopting MT to transform thermophilic digesters into mesophilic digesters is feasible and could potentially enhance the further optimization and broader application of practical anaerobic engineering.

Long-term observations on the hydraulic performance of a combined capillary barrier-methane oxidation landfill cover system.

This study quantifies the field hydraulic performance of a dual-functionality landfill cover, combining microbial methane oxidation with water diversion using a capillary barrier. The investigated 500 m2 test field, constructed on a landfill in the Netherlands, consisted of a cover soil optimised for methane oxidation, underlain by a sandy capillary layer and a gravelly capillary block. Outflows from these layers were measured between 2009 and 2023. Average precipitation was 848 mm/a, evapotranspiration, diverted infiltration and breakthrough amounted to 504 (59.4 %), 282 (33.3 %) and 62 (7.3 %) mm/a, respectively. On average, the capillary barrier diverted 82 % of the inflow into the capillary layer. Breakthrough occurred mainly from October to March when evapotranspiration was low and the maximum water storage capacity of the cover soil was reached. During this period, inflow into the capillary barrier exceeded its diversion capacity, caused by the relatively high hydraulic conductivity of the cover soil due to its optimisation for gas transport. The diversion capacity declined drastically in the year after construction and increased again afterwards. This was attributed to suffusion of sand from the capillary layer into the capillary block and subsequent washout to greater depths or the influence of iron precipitates at the bottom of the capillary layer. The effect of a more finely grained methane oxidation layer on the hydraulic and methane oxidation performance should be investigated further. These measures could further improve the combined performance of the dual functionality landfill cover system under the given conditions of a temperate climate.

Effect of Padina gymnospora biowaste inclusion on in vitro methane production, feed fermentation, and microbial diversity.

In vitro studies were undertaken aiming to study the methane (CH4) mitigation potential of biowaste (BW) of Padina gymnospora at the graded inclusion of 0% (C), 2% (A2), 5% (A5), and 10% (A10) of the diet composed of straw and concentrate in 40:60 ratio. The chemical composition analysis revealed that the BW contained higher crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), and ether extract (EE) than the PF (fresh seaweed, P. gymnospora). The concentration of cinnamic acid, sinapic acid, kaempferol, fisetin p-coumaric acid, ellagic acid, and luteolin in BW was 1.5-6-folds less than the PF. Inclusion of BW decreased (P < 0.0001) CH4 production by 34%, 38%, and 45% in A2, A5, and A10 treatments, respectively. A decrease (P < 0.0001) of 7.5%-8% in dry matter (DM) and organic matter (OM) digestibility was also recorded with the BW supplementation. The BW inclusion also decreased the numbers of total (P = 0.007), Entodinomorphs (P = 0.011), and Holotrichs (P = 0.004) protozoa. Metagenome data revealed the dominance of Bacteroidetes, Proteobacteria, Firmicutes, Actinobacteria, and Fibrobacter microbial phyla. At the phylum level, Euryarchaeota dominated the archaeal community, whereas Methanobrevibacter was most abundant at the genus level. It can be concluded that the inclusion of BW in straw and concentrate based diet by affecting rumen fermentation, protozoal numbers, and compositional shift in the archaeal community significantly decreased CH4 production. Utilization of biowaste of P. gymnospora as a CH4 mitigating agent will ensure its efficient utilization rather than dumping, which shall cause environmental pollution and health hazards.

Effects of long-term exposure to zinc on performances of anaerobic digesters for swine wastewater treatment under various organic loading rates.

The long-term performance of anaerobic digestion (AD) often decreases substantially when treating swine wastewater contaminated with heavy metals. However, the toxicological characteristics and mechanisms of continuous exposure to heavy metals under different organic loading rates (OLR) are still poorly understood. In these semi-continuous AD experiments, it was found that zinc concentrations of 40 mg/L only deteriorated the reductive environments of AD. In comparison, a concentration of 2.0 mg/L probably facilitated the reproduction of microorganisms in the operating digesters with a constant OLR of 0.51 g COD/(L·d). Nevertheless, when the OLR was increased to 2.30 g COD/(L·d), 2.0 mg/L zinc inhibited various life activities of microorganisms at the molecular level within only 10 days. Hence, even though 2.0 mg/L zinc could promote AD performances from a macroscopic perspective, it had potential inhibitory effects on AD. Therefore, this study deepens the understanding of the inhibitions caused by heavy metals on AD and the metabolic laws of anaerobic microorganisms in swine wastewater treatment. These results could be referred to for enhancing AD in the presence of zinc in practical swine wastewater treatment.

Methane gas in breath test is associated with non-alcoholic fatty liver disease.

Although the associations between a patient's body mass index (BMI) and metabolic diseases, as well as their breath test results, have been studied, the relationship between breath hydrogen/methane levels and metabolic diseases needs to be further clarified. We aimed to investigate how the composition of exhaled breath gases relates to metabolic disorders, such as diabetes mellitus, dyslipidemia, hypertension, and nonalcoholic fatty liver disease (NAFLD), and their key risk factors. An analysis was performed using the medical records, including the lactulose breath test (LBT) data of patients who visited the Ajou University Medical Center, Suwon, Republic of Korea, between January 2016 and December 2021. The patients were grouped according to four different criteria for LBT hydrogen and methane levels. Of 441 patients, 325 (72.1%) had positive results for methane only (hydrogen < 20 parts per million [ppm] and methane ⩾ 3 ppm). BMIs and NAFLD prevalence were higher in patients with only methane positivity than in patients with hydrogen and methane positivity (hydrogen ⩾ 20 ppm and methane ⩾ 3 ppm). According to a multivariate analysis, the odds ratio of only methane positivity was 2.002 (95% confidence interval [CI]: 1.244-3.221,P= 0.004) for NAFLD. Our results demonstrate that breath methane positivity is related to NAFLD and suggest that increased methane gas on the breath tests has the potential to be an easily measurable biomarker for NAFLD diagnosis.

Catalytic methane decomposition on CNT-supported Fe-catalysts.

Methane, either as natural gas or as a resource obtained from various bioprocesses (e.g., digestion, landfill) can be converted to carbon and hydrogen according to. CH4(g)→C(s)+2H2(g)ΔH298K=74.8kJ/mol. Previous research has stressed the growing importance of substituting the high-temperature Steam Methane Reforming (SMR) by a moderate temperature Catalytic Methane Decomposition (CMD). The carbon formed is moreover of nanotube nature, in high industrial demand. To avoid the use of an inert support for the active catalyst species, e.g., Al2O3 for Fe, leading to a progressive contamination of the catalyst by support debris and coking of the catalyst, the present research investigates the use of carbon nanotubes (CNTs) as Fe-support. Average CH4 conversions of 75-85% are obtained at 700 °C for a continuous operation of 40 h. The produced CNT from the methane conversion can be continuously removed from the catalyst bed by carry-over due to its bulk density difference (∼120 kg/m3) with the catalyst itself (∼1500 kg/m3). CNT properties are fully specified. No thermal regeneration of the catalyst is required. A tentative process layout and economic analysis demonstrate the scalability of the process and the very competitive production costs of H2 and CNT.

Multipressure Sampling for Improving the Performance of MOF-based Electronic Noses.

Metal-organic frameworks (MOFs) are a promising class of porous materials for the design of gas sensing arrays, which are often called electronic noses. Due to their chemical and structural tunability, MOFs are a highly diverse class of materials that align well with the similarly diverse class of volatile organic compounds (VOCs) of interest in many gas detection applications. In principle, by choosing the right combination of cross-sensitive MOFs, layered on appropriate signal transducers, one can design an array that yields detailed information about the composition of a complex gas mixture. However, despite the vast number of MOFs from which one can choose, gas sensing arrays that rely too heavily on distinct chemistries can be impractical from the cost and complexity perspective. On the other hand, it is difficult for small arrays to have the desired selectivity and sensitivity for challenging sensing applications, such as detecting weakly adsorbing gases with weak signals, or conversely, strongly adsorbing gases that readily saturate MOF pores. In this work, we employed gas adsorption simulations to explore the use of a variable pressure sensing array as a means of improving both sensitivity and selectivity as well as increasing the information content provided by each array. We studied nine different MOFs (HKUST-1, IRMOF-1, MgMOF-74, MOF-177, MOF-801, NU-100, NU-125, UiO-66, and ZIF-8) and four different gas mixtures, each containing nitrogen, oxygen, carbon dioxide, and exactly one of the hydrogen, methane, hydrogen sulfide, or benzene. We found that by lowering the pressure, we can limit the saturation of MOFs, and by raising the pressure, we can concentrate weakly adsorbing gases, in both cases, improving gas detection with the resulting arrays. In many cases, changing the system pressure yielded a better improvement in performance (as measured by the Kullback-Liebler divergence of gas composition probability distributions) than including additional MOFs. We thus demonstrated and quantified how sensing at multiple pressures can increase information content and cross-sensitivity in MOF-based arrays while limiting the number of unique materials needed in the device.

Eutrophication driven macrophyte-derived organic matter decomposition to methane emission relates to co-metabolism effect in freshwater sediments.

Lakes and wetlands play pivotal roles in global organic matter storage, receiving significant inputs of organic material. However, the co-metabolic processes governing the decomposition of these organic materials and their impact on greenhouse gas emissions remain inadequately understood. This study aims to assess the effects of mixed decomposition involving macrophytes and cyanobacteria on carbon emissions. A series of microcosms was established to investigate the decomposition of macrophyte residues and algae over a period of 216 days. A two-component kinetic model was utilized to estimate methane (CH4) production rates. Gas isotope technology was employed to discern the contributions of CH4 produced by macrophyte residues or algae. Quantitative PCR and analysis of 16S rRNA gene amplicons were employed to assess changes in functional genes and microbial communities. There were significant differences in the cumulative carbon release from the decomposition of different plant types due to the addition of carbon sources. After adding algae, the cumulative emission of CH4 increased significantly. The δ13C-CH4 partitioning indicated that CH4 originated exclusively from the fresh organic carbon of macrophyte residues, while it shifted to algae source after adding algae. The synergistic effect of the mixed decomposition on the CH4 emissions was greater than the sum of the individual decompositions. The microbial community richness was higher in the single plant residue treatment compared to the mixed treatment with algae addition, while microbial evenness in the sediment increased steadily in each treatment. Our findings emphasize the pronounced co-metabolic effect observed during the mixed decomposition of macrophytes and cyanobacteria.

Biochar alleviates inhibition effects of humic acid on anaerobic digestion: Insights to performances and mechanisms.

To recover methane from waste activated sludge through anaerobic digestion (AD) is one promising alternative to achieve carbon neutrality for wastewater treatment plants. However, humic acids (HAs) are one of the major compositions in waste activated sludge, and their accumulation performs inhibition effects on AD. This study investigated the potentials of biochar (BC) in alleviating inhibition effects of HAs on AD. Results showed that although the accumulated HAs reduced methane yield by 9.37% compared to control, the highest methane yield, 132.6 mL CH4/g VSS, was obtained after adding BC, which was 45.9% higher than that in HA group. Mechanism analysis showed that BC promoted the activities of hydrolase such as protease and α-glucosidase, which were 69.7% and 29.7% higher than those in HA group, respectively. The conversion of short-chain fatty acids was accelerated. In addition, the evolutions of electroactive microorganisms like Clostridium_sensu_stricto_13 and Methanosaeta were consistent with the activitiies of electron transfer and the contents of cytochrome c. Furthermore, parts of HAs rather than all of them were adsorbed by BC, and the remaining free HAs and BC formed synergistic effects on methanogenesis, then both CO2 reduction and acetoclastic methanogenesis pathways were improved. The findings may provide some solutions to alleviate inhibition effects of HAs on AD.

Methane Quantification Performance of the Quantitative Optical Gas Imaging (QOGI) System Using Single-Blind Controlled Release Assessment.

Quantitative optical gas imaging (QOGI) system can rapidly quantify leaks detected by optical gas imaging (OGI) cameras across the oil and gas supply chain. A comprehensive evaluation of the QOGI system's quantification capability is needed for the successful adoption of the technology. This study conducted single-blind experiments to examine the quantification performance of the FLIR QL320 QOGI system under near-field conditions at a pseudo-realistic, outdoor, controlled testing facility that mimics upstream and midstream natural gas operations. The study completed 357 individual measurements across 26 controlled releases and 71 camera positions for release rates between 0.1 kg Ch4/h and 2.9 kg Ch4/h of compressed natural gas (which accounts for more than 90% of typical component-level leaks in several production facilities). The majority (75%) of measurements were within a quantification factor of 3 (quantification error of -67% to 200%) with individual errors between -90% and 831%, which reduced to -79% to +297% when the mean of estimates of the same controlled release from multiple camera positions was considered. Performance improved with increasing release rate, using clear sky as plume background, and at wind speeds ≤1 mph relative to other measurement conditions.

CH4 production potential of autotrophic nitrification bacteria produced in the submerged nitrification bioreactor in the laboratory and kinetic analysis.

In this study, CH4 production capacity of nitrification bacteria (NB) obtained from the submerged biofilter in the laboratory was investigated. Biochemical methane potential (BMP) test was carried out with the NB amount of zero (control, CR), 5% (R1), 10% (R2), and 15% (R3) at a temperature of about 37 ± 0.5°C. Compared to the CR, significantly higher cumulative CH4 volume of about 290, 490, and 715 mL were determined in the R1, R2, and R3, respectively. All the applied kinetic models gave good results (R2 ≥0.97), while the Transference Function and First-order models provided the better R2 values. The delay phase (λ) was not observed in the AD process, and CH4 production started immediately on the first day of operation. The predicted k value of 0.133 day-1 was high in CR, while it was approximately between 0.078 and 0.112 day-1 for the higher amount of NB containing BMP units, which indicated that the AD required long reaction time.

Comparison of anaerobic co-digestion of vacuum toilet blackwater and kitchen waste under mesophilic and thermophilic conditions: Reactor performance, microbial response and metabolic pathway.

Co-digestion of kitchen waste (KW) and black water (BW) can be considered as an attractive method to efficiently achieve the clean energy from waste. To find the optimal operation parameters for the co-digestion, the effects of different temperatures (35 and 55 °C) and BW:KW ratios on the reactor performances, microbial communities and metabolic pathways were studied. The results showed that the optimum BW:KW ratio was 1:3.6 and 1:4.5 for mesophilic and thermophilic optimal reactors, with methane production of 449.04 mL/g VS and 411.90 mL/g VS, respectively. Microbial communities showed significant differences between the reactors under different temperatures. For bacteria, increasing BW:KW ratio significantly promoted Defluviitoga enrichment (1.1%-9.5%) under thermophilic condition. For Archaea, the increase in BW:KW ratio promoted the enrichment of Methanosaeta (8.6%-56.4%) in the mesophilic reactor and Methanothermobacter (62.0%-89.2%) in the thermophilic reactor. The analysis of the key enzymes showed that, acetoclastic methanogenic pathway performed as the dominant under mesophilic condition, with high abundance of Acetate-CoA ligase (EC:6.2.1.1) and Pyruvate synthase (EC:1.2.7.1). Hydrogenotrophic methanogenic pathway was the main pathway in the thermophilic reactors, with high abundance of Formylmethanofuran dehydrogenase (EC:1.2.99.5).

The effect of raw material (cow and chicken manure) and reactor type for improving and maximizing biogas production.

Biomass energy is a type of renewable energy and animal waste is one of the main resources for its production. The purpose of this study is to investigate the effect of raw material type (cow and chicken manure) and the type of reactor (digester) on the biogas produced by measuring the amount of methane in the product. Three types of digester (metal, simple PVC, and PVC with leachate rotation) with the same volume (10 L) were prepared. Equipment was installed on the digesters to measure the pH and volume of produced gas. The experiments were carried out in controlled temperature conditions (28-30 °C) and in two stages. The first experiment was to load the digesters with cow excrement, and the second experiment was to load the digesters with chicken excrement. In both experiments, the digesters were fed with 1.5 kg of animal manure and water with a ratio of 1:1. During a period of 60 days, the volume of biogas and methane produced was measured and recorded. The results showed that the amount of biogas produced from chicken waste is more than the amount obtained from cow waste. However, the amount of methane produced using cow excrement was more than that of chicken excrement. Also, the performance of PVC digester with leachate rotation was better than the other two digesters, which could be due to the mixing of raw materials in this type of digester.